In the category of symmetric graphs there are exactly five closed tensor products. If we omit the requirement of units, we obtain twelve more.
@article{116973, author = {Wilfried Imrich and Ale\v s Pultr}, title = {Classification of tensor products of symmetric graphs}, journal = {Commentationes Mathematicae Universitatis Carolinae}, volume = {32}, year = {1991}, pages = {315-322}, zbl = {0755.18001}, mrnumber = {1137793}, language = {en}, url = {http://dml.mathdoc.fr/item/116973} }
Imrich, Wilfried; Pultr, Aleš. Classification of tensor products of symmetric graphs. Commentationes Mathematicae Universitatis Carolinae, Tome 32 (1991) pp. 315-322. http://gdmltest.u-ga.fr/item/116973/
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